1. Cross-Reference to Related Applications
This invention uses the UME of co-pending application, Apparatus and Method for Providing a Usefulness Metric based on Coding Information for Video Enhancement, inventors Lilla Boroczky and Johan Janssen, filed concurrently herewith.
2. Field of the Invention
The present invention is directed to a system and method for enhancing the sharpness of encoded/transcoded digital video, without enhancing encoding artifacts, which has particular utility in connection with spatial domain sharpness enhancement algorithms used in multimedia devices.
3. Description of the Related Art
The development of high-quality multi-media devices, such as set-top boxes, high-end TV's, Digital TV's, Personal TV's, storage products, PDA's, wireless internet devices, etc., is leading to a variety of architectures and to more openness towards new features for these devices. Moreover, the development of these new products and their ability to display video data in any format, has resulted in new requirements and opportunities with respect to video processing and video enhancement algorithms. Most of these devices receive and/or store video in the MPEG-2 format and in the future they may receive/store in the MPEG-4 format. The picture quality of these MPEG sources can vary between very good and extremely bad.
Next generation storage devices, such as the blue-laser-based Digital Video Recorder (DVR) will have to some extent HD (ATSC) capability and are an example of the type of device for which a new method of picture enhancement would be advantageous. An HD program is typically broadcast at 20 Mb/s and encoded according to the MPEG-2 video standard. Taking into account the approximately 25 GB storage capacity of the DVR, this represents about a two-hour recording time of HD video per disc. To increase the record time, several long-play modes can be defined, such as Long-Play (LP) and Extended-Long-Play (ELP) modes.
For LP-mode the average storage bitrate is assumed to be approximately 10 Mb/s, which allows double record time for HD. As a consequence, transcoding is an integral part of the video processing chain, which reduces the broadcast bitrate of 20 Mb/s to the storage bitrate of 10 Mb/s. During the MPEG-2 transcoding, the picture quality (e.g., sharpness) of the video, is most likely reduced. However, especially for the LP mode, the picture quality should not be compromised too much. Therefore, for the LP mode, post-processing plays an important role in improving the perceived picture quality.
To date, most of the state-of-the-art sharpness enhancement algorithms were developed and optimized for analog video transmission standards like NTSC, PAL and SECAM. Traditionally, image enhancement algorithms either reduce certain unwanted aspects in a picture (e.g., noise reduction) or improve certain desired characteristics of an image (e.g., sharpness enhancement). For these emerging storage devices, the traditional sharpness enhancement algorithms may perform sub-optimally on MPEG encoded or transcoded video due to the different characteristics of these sources. In the closed video processing chain of the storage system, information which allows for determining the quality of the encoded source can be derived from the MPEG stream. This information can potentially be used to increase the performance of image enhancement algorithms.
Because image quality will remain a distinguishing factor for high-end video products, new approaches for performing image enhancement, specifically adapted for use with these sources, will be beneficial. In C-J Tsai, P. Karunaratne, N. P. Galatsanos and A. K. Katsaggelos, “A Compressed Video Enhancement Algorithm”, Proc. of IEEE, ICIP'99, Kobe, Japan, Oct. 25-28, 1999, the authors propose an iterative algorithm for enhancing video sequences that are encoded at low bit rates. For MPEG sources, the degradation of the picture quality originates mostly from the quantization function. Thus, the iterative gradient-projection algorithm employed by the authors uses coding information such as quantization step size, macroblock types and forward motion vectors in its cost function. The algorithm shows promising results for low bit rate video, however its main disadvantage is its high computational complexity.
In B. Martins and S. Forchammer, “Improved Decoding of MPEG-2 Coded Video”, Proc. of IBC′2000, Amsterdam, The Netherlands, Sep. 7-12, 2000, pp. 109-115, the authors describe a new concept for improving the decoding of MPEG-2 coded video. Specifically, a unified approach for deinterlacing and format conversion, integrated in the decoding process, is proposed. The technique results in considerably higher picture quality than that obtained by ordinary decoding. However, to date, its computational complexity prevents its implementation in consumer applications.
Both papers describe video enhancement algorithms using MPEG coding information and a cost function. However, both of these scenarios, in addition to being impractical, combine the enhancement and the cost function. A cost function determines how much, and at which locations in a picture, enhancement can be applied. The problem which results from this combination of cost and enhancement functions is that only one algorithm can be used with the cost function.